1. Field of the Invention
The present invention relates to a golf club head and a process for producing the same, and more particularly relates to improvements in mechanical properties and production of a hollow metallic golf club head of a metal wood or the like.
2. Description of the Related Art
A golf club head of this type has a planar face and a round body section including a sole, crown, heel and toe. Such a metal golf club head has conventionally been produced by precision casting from metals such a stainless steel alloys, aluminum alloys, titanium alloys and beryllium-copper alloys. Production by castings is, however, inevitably accompanied with segregation of components, generation of casting defects and coarse state of crystal particles which often exceed 0.5 mm in diameter. These factors in production usually result in poor proof stress and tensile strength of the product. Due to such low mechanical properties, it is difficult to provide the conventional metal golf club head with a thin shell construction. That is, increase in club head size unavoidably entails a thick shell construction which naturally increases the weight of the golf club head.
Thus, for the purpose of reduction in weight, a conventional metal golf club head is forced to assume a small dimension which allows provision of a very small sweet area only, thereby lowering the directional stability of the golf club head. That is, a ball struck by the golf club head does not fly correctly in the direction intended by its user.
As a substitute for such production by casting, a plastic process such as forging and pressing has lately been developed. More specifically, several pieces such as a face and a body section are first prepared by a plastic process and next joined together via, for example, welding to form a hollow main body of a metal golf club head. The body section is usually made up of two or more pieces which are joined together prior to joining to the face.
More specifically in real production via the plastic process, separate section models are prepared copying the shapes of the face, the crown and the sole of a golf club head to be produced. Next the section models are assembled together to form a hollow metallic mold. After placing an alloy plate, e.g., a Ti alloy plate, in position within the metallic mold, the mold with the alloy plate is heated up to, for example, 950.degree. C. with concurrent introduction of high pressure inert gas such as Ar gas in order to press the alloy plate against the inner wall of the metallic mold. After continued heating for about 60 min. the shaped parts are taken out of the mold for subsequent surface finishing. A part copying the face is prepared by a separate cutting process. The parts thus prepared are joined together via welding to a golf club head main body which is then assembled with a hosel to form a golf club head.
The golf club head produced by the plastic process is free from various troubles caused by the casting process, but is still accompanied by several drawbacks mainly caused by welding employed in production for joining the shaped parts. When striking balls, the face of the golf club head warps significantly and, as a consequence, high compressive stress acts on the welded junction between the face and the body section. The welded junction is additionally exposed to bending stress which is also caused by warping of the face when striking balls. Thus, the welded junction is rather poor in mechanical durability.
Further during production, the face and the body section are prepared by separate plastic processes and joined together thereafter via welding. This joining via welding tends to lower the dimensional accuracy of the product and the separate preparation apparently lowers production efficiency.